Method for starting up a gas and steam turbine system

ABSTRACT

A method for starting a gas and steam turbine system which includes a gas turbine system which includes at least one gas turbine, in addition to at least one steam turbine system which includes at least one steam turbine and at least one steam system is provided. Heat produced by the working fluid and which is released in the gas turbine is guided to the steam system in order to produce steam which drives the steam turbine. During starting, the gas turbine is started prior to the steam turbine and the steam turbine is started in the presence of the first steam in the system and is impinged upon by said steam.

CROSS REFERENCE TO RELATED APPLICATIONS

This a continuation application which claims benefit of the U.S.National Stage application 11/887,868 filed Oct. 4, 2007. The USNational Stage application claims benefit to International ApplicationNo. PCT/EP2006/061217, filed Mar. 31, 2006. The InternationalApplication claims priority to European application No. 05007416.0 filedApr. 5, 2005. All of the applications are incorporated by referenceherein in their entirety.

FIELD OF INVENTION

The present invention relates to a method for starting up a gas andsteam turbine system, and in particular a method for a fast startup of asystem of said kind.

BACKGROUND OF THE INVENTION

In a gas turbine system a gaseous or liquid fuel, for example naturalgas or crude oil, is mixed with compressed air and combusted. Thepressurized combustion exhaust gases are supplied to the turbine of thegas turbine system as the working medium. The working medium sets theturbines under expansion into rotation, with thermal energy beingconverted into mechanical work, i.e. the rotation of the turbine shaft.When the expanded working medium is discharged from the gas turbinesystem said medium typically still has a temperature of 500-600° C.

In a gas and steam turbine system the expanded working medium, alsocalled flue gas, from the gas turbine system is used to generate steamfor driving a steam turbine. Toward that end the working medium issupplied to a heat recovery steam generator connected downstream of thegas turbine system on the exhaust gas side, in which steam generatorheating surfaces are arranged in the form of pipes or pipe bundles. Saidheating surfaces are in turn connected into a water-steam cycle of thesteam turbine system which has at least one, but mostly a plurality ofpressure stages. The pressure stages differ from one another in that thewater supplied to the heating surface for the purpose of generatingsteam has different pressure levels. A gas and steam turbine systemcomprising a water-steam cycle having only one pressure stage isdescribed in DE 197 36 888 A1, and such a system comprising threepressure stages, namely a high-pressure stage, a medium-pressure stageand a low-pressure stage, is described in DE 100 04 187 C1.

Currently, in order to start a gas and steam turbine system, the gasturbine system is usually started up and the expanded working medium issupplied to the heat recovery steam generator of the steam turbinesystem. Initially, however, the steam generated in the heat recoverysteam generator is not fed to the turbine part of the steam turbinesystem, but is directed past the turbine via diverter stations andsupplied directly to a condenser which condenses the steam to water. Thecondensate is then supplied to the steam generator again as feedwater.In many embodiment variants of gas and steam turbine systems thediverted steam is also conveyed to the atmosphere.

The steam turbine is only switched into the cycle when certain steamparameters in the steam lines of the water-steam cycle or in the steamlines leading to the turbine part of the gas turbine system, for examplecertain steam pressures and temperatures, are complied with. Complyingwith said steam parameters is designed to keep potential stresses inthick-walled components at a low level.

After the startup of the gas turbine system there is a power increasewhich leads to an increase in pressure in the steam system. The loadgradient at which the gas turbine system is started up, i.e. the powerincrease of the gas turbine system per time unit, is criticallydependent on the implementation and mode of construction of the heatrecovery steam generator as well as on the structural limitations withinthe steam turbine. As the gas turbine load and consequently thetemperature or, as the case may be, the volume flow rate of the exhaustgas emitted from the gas turbine system increase, the steam temperatureand the pressure in the steam system are also increased.

Before the steam turbine starts up, the gas turbine is typically kept ata specific partial load until stationary states have come about in thegas turbine system and in the steam system. As soon as stable steamproduction has been reached, the steam contained in the steam system ischanneled to the steam turbine, thereby accelerating the steam turbine.The turbine speed is then increased to nominal speed. Followingsynchronization of the generator coupled to the steam turbine with thepower supply system, or in the case of single-shaft systems, followingthe engagement of the overrunning clutch, the steam turbine is subjectedto further load as a result of an increase in the steam supply. At thesame time the diverter stations close more and more in order to keep thesteam pressure roughly constant and minimize level fluctuations in theheat recovery steam generator.

As soon as the diverter stations are closed and the steam produced inthe heat recovery steam generator is channeled in its entirety to thesteam turbine, a further increase in the gas turbine power output takesplace when there is a higher power requirement on the part of the systemwhich is now operating in the gas and steam turbine mode.

By definition, the startup operation of a gas and steam turbine systemis terminated only when the gas turbine has reached the base load andall diverter stations are closed.

SUMMARY OF INVENTION

The object of the present invention is to provide a method for startingup a gas and steam turbine system which enables a faster startupoperation than the method described in the introduction.

This object is achieved by means of a method for starting up a gas andsteam turbine system as claimed in the claims. The dependent claimscontain advantageous embodiments of the method.

According to the invention, a method is provided for starting up a gasand steam turbine system, in particular for fast starting up of a gasand steam turbine system which has a gas turbine system comprising atleast one gas turbine as well as a steam turbine system having at leastone steam turbine and at least one steam system and in which the wasteheat of a working medium expanding in the gas turbine is supplied to thesteam system for the purpose of generating the steam driving the steamturbine.

In the method according to the invention, at startup time the gasturbine is started first, before the steam turbine is started. The steamturbine is then already started up when the first steam is present inthe steam system and is impinged upon by steam.

In the method according to the invention, the steam turbine is startedup at the earliest possible time and accelerated by means of the firststeam from the heat recovery steam generator, without waiting forstationary states in the steam system. This measure enables the startupoperation of the gas and steam turbine system to be shortenedconsiderably.

In contrast to the usual startup method, the steam temperature in thesteam system at the time of starting the steam turbine can be less thanthe material temperature of the steam turbine or of its housing. Theearly channeling of the steam to the steam turbine can therefore lead toa cooling down of the components and to thermal stresses. However, acertain compensation can be achieved if the gradients are keptcorrespondingly low during the following increase in the steamtemperatures.

Advantageously, the tuning of the steam system during the startupoperation is chosen in such a way that the steam pressure increasescontinuously. This can be achieved, for example, by opening a steamdiverter station of the steam system only so wide that a minimum steamquantity required for accelerating and/or synchronizing the steamturbine is generated using a part of the waste heat of the workingmedium and a pressure increase in the steam system is produced by meansof the remaining part of the waste heat of the working medium.

In addition to a pressure increase in the steam system, thecomparatively small opening of the steam diverter station leads to areduction in the steam production in the heat recovery steam generator.As a result the thermal load to the condenser is reduced and thediverter station can close more quickly.

In a special embodiment of the method according to the invention thediverter station is not opened at all.

The method according to the invention can be embodied in particular insuch a way that the gas turbine system experiences a load increaseduring the entire startup operation, in particular until the base loadis reached. In other words, the method dispenses with keeping the gasturbine system at a certain partial load and waiting until the gasturbine system and the steam system of the steam turbine system havesettled into stationary states. This measure also leads to a reductionin the startup time of the gas turbine system and thus enables a faststartup.

In a special embodiment the gas turbine system's load is increased atmaximum load ramp, which is to say that there is a maximum increase inthe gas turbine power output per time unit.

The gas and steam turbine system during the starting up of the gasturbine system to base load is preferably switched over into the gas andsteam turbine operating mode, with the result that the startup operationis, by definition, terminated when the gas turbine base load is reached.The switchover into the gas and steam turbine operating mode can includein particular the synchronization of a generator coupled to the steamturbine with the power supply system or, in the case of single-shaftsystems, the engagement of the automatic overrunning clutch.

The described method according to the invention for starting up a gasand steam turbine system shortens the startup time of the systemconsiderably. Compared with the method described in the introduction, areduction in the starting time by approximately 50% is achievable. A gasand steam turbine operator can therefore respond very flexibly toshort-term requirements, as a result of which the revenues from thepurchase of power can be increased. As a result of the early steamtakeover of the steam turbine and the reduced thermal load in thecondenser, which leads to smaller power losses, there is also anincrease in the averaged efficiency of the gas and steam turbine system,which is a significant factor in particular in the case of frequentstarts and increases the cost-effectiveness of the system.

Moreover, the lower steam production in the method according to theinvention for starting up a gas and steam turbine system also enablessmaller diverter stations to be installed, thereby reducing investmentcosts.

The described startup method enabling a fast startup of a gas and steamturbine system can essentially be realized by means of softwaremodifications. It is therefore also possible to convert existing gas andsteam turbine systems to the startup method according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, characteristics and advantages of the presentinvention will emerge from the following description of an exemplaryembodiment with reference to the accompanying figure.

FIG. 1 shows a schematic diagram for a gas and steam turbine system.

DETAILED DESCRIPTION OF INVENTION

The gas and steam turbine system 1 represented schematically in FIG. 1comprises a gas turbine system 1 a as well as a steam turbine system 1b. The gas turbine system 1 a is equipped with a gas turbine 2, acompressor 4, and at least one combustion chamber 6 connected betweenthe compressor 4 and the gas turbine 2. By means of the compressor 4,fresh air L is drawn in, compressed and supplied via the fresh air line8 to one or more burners of the combustion chamber 6. The supplied airis mixed with liquid or gaseous fuel B fed via a fuel line 10 and themixture ignited. The resulting combustion exhaust gases form the workingmedium AM of the gas turbine system 1 a, which working medium AM issupplied to the gas turbine 2, where it produces work under expansionand drives a shaft 14 coupled to the gas turbine 2. The shaft 14 iscoupled not only to the gas turbine 2 but also to the air compressor 4as well as to a generator 12 in order to drive the latter. The expandedworking medium AM is conducted via an exhaust gas line 34 to a heatrecovery steam generator 30 of the steam turbine system 1 b.

In the heat recovery steam generator 30 the working medium output by thegas turbine 1 a at a temperature of approx. 500-600° C. is used forgenerating and superheating steam.

In addition to the heat recovery steam generator 30, which can beembodied in particular as a once-through, forced-flow system, the steamturbine system 1 b comprises a steam turbine 20 having turbine stages 20a, 20 b, 20 c and a condenser 26. The heat recovery steam generator 30and the condenser 26, in combination with condensate lines and feedwaterlines 35, 40 as well as steam lines 48, 53, 64, 70, 80, 100, form asteam system which, together with the steam turbine 20, forms awater-steam cycle.

Water from a feedwater reservoir 38 is supplied by means of a feedwaterpump 42 to a high-pressure preheater 44, also known as an economizer,and from there is forwarded to an evaporator 46 which is designed foronce-through operation and is connected to the economizer 44 on theoutput side. For its part, the evaporator 46 is in turn connected on theoutput side to a superheater 52 via a steam line 48 into which a waterseparator 50 is inserted. The superheater 52 is connected on the outputside via a steam line 53 to the steam input 54 of the high-pressurestage 20 a of the steam turbine 20.

In the high-pressure stage 20 a of the steam turbine 20, the superheatedsteam from the superheater 52 drives the turbine before it is passed onvia the steam output 56 of the high-pressure stage 20 a to anintermediate superheater 58.

After being superheated in the intermediate superheater 58, the steam isforwarded via a further steam line 81 to the steam input 60 of themedium-pressure stage 20 b of the steam turbine 20, where it drives theturbine.

The steam output 62 of the medium-pressure stage 20 b is connected viaan overflow line 64 to the steam inlet 66 of the low-pressure stage 20 cof the steam turbine. After flowing through the low-pressure stage 20 cand the driving of the turbine associated therewith, the cooled andexpanded steam is output via the steam output 68 of the low-pressurestage 20 c to the steam line 70, which leads it to the condenser 26.

The condenser 26 converts the incoming steam into condensate andforwards the condensate by means of a condensate pump 36 to thefeedwater reservoir 38 via the condensate line 35.

In addition to the already mentioned elements of the water-steam cycle,the latter also comprises a bypass line 100, what is referred to as thehigh-pressure diverter line, which branches off from the steam line 53before the latter reaches the steam inlet 54 of the high-pressure stage20 a. The high-pressure bypass line 100 bypasses the high-pressure stage20 a and flows into the feed line 80 to the intermediate superheater 58.A further bypass line, referred to as the medium-pressure bypass line200, branches from the steam line 81 before the latter flows into thesteam inlet 60 of the medium-pressure stage 20 b. The medium-pressurebypass line 200 bypasses both the medium-pressure stage 20 b and thelow-pressure stage 20 c and flows into the steam line 70 leading to thecondenser 26.

Incorporated into the high-pressure bypass line 100 and themedium-pressure bypass line 200 are the shutoff valves 102, 202, bymeans of which said lines can be shut off. Shutoff valves 104, 204 arealso included in the steam line 53 and in the steam line 81, in eachcase between the branching-off point of the bypass line 100 and 200,respectively, and the steam inlet 54 of the high-pressure stage 20 a andthe steam inlet 60 of the medium-pressure stage 20 a, respectively.

Incorporated into the medium-pressure bypass line 200 is a shutoff valve202 by means of which said line can be shut off. A shutoff valve 104 isalso included in the steam line 53, namely between the branching-offpoint of the bypass line 100 and the steam inlet 54 of the high-pressurestage 20 a of the steam turbine 20.

The bypass line 100 and the shutoff valves 102, 104 are used during thestarting up of the gas and steam turbine system 1 to divert a part ofthe steam for the purpose of bypassing the steam turbine 2. It ispossible for at least one diverter station 100, 102, 200, 202 to beopened only so wide that a minimum steam quantity required foraccelerating and/or synchronizing the steam turbine 20 is generated by apart of the waste heat of the working medium and an increase in pressureis produced in the steam system by the remainder of the waste heat ofthe working medium It is further possible that no diverter station 100,102, 200, 202 leading to a bypassing of the steam turbine is opened inthe steam system.

An exemplary embodiment of the method according to the invention forstarting up a gas and steam turbine system is described below based onthe system 1 described with reference to FIG. 1.

At the start of the method the gas turbine system la is started and theworking medium AM being discharged from the system is supplied to theheat recovery steam generator 30 via an input 30 a. The expanded workingmedium AM flows through the heat recovery steam generator 30 and exitsthe latter via an output 30 b in the direction of a vent stack (notshown in FIG. 1). As the working medium AM flows through the heatrecovery steam generator 30, heat is transferred from the working mediumAM to the water or steam in the water-steam cycle.

After the gas turbine system has been started up, the waste heat of theworking medium in the heat recovery steam generator 30 leads to thestart of steam production in the steam system.

In this early phase of the startup operation the shutoff valves 102 and104 or 202 and 204 are set in such a way that only a small part of thegenerated steam flows through the bypass lines 100, 200 and already inthis phase of the startup operation the majority of the steam issupplied to the steam turbine 20. The part of the steam supplied to thesteam turbine 20 accelerates the steam turbine and preheats the latterinsofar as the steam is hotter than the material of the turbine and thesteam lines.

Since only a small amount of steam flows directly to the condenser 26via the medium-pressure bypass line 200, the waste heat not used duringthe acceleration and preheating of the steam turbine 20 leads to apressure increase in the steam system. In the further course of thestartup operation the steam pressure therefore increases continuously inthe steam system, as a result of which steam production in the heatrecovery steam generator is reduced. This leads to a reduction in theheat input into the condenser 26 and as a result the shutoff valves 102and 202, which are not fully open anyway, can be closed quickly comparedto prior art starting methods.

Once the gas turbine system 1 a has been started, the load of the gasturbine system is increased preferably at maximum load ramp until thebase load is reached.

If the steam temperature is less than the material temperature of theturbine 20 at the start of the introduction of steam into the steamturbine 20, the steam temperature will steadily increase during thestartup of the load of the gas turbine system and relatively soon exceedthe material temperature of the steam turbine and the lines leadingthereto. If the rapid rise from a relatively cool temperature of theturbine components to a high temperature would exceed a certainpredefined limit of the thermal stresses in the material due to thestarting up of the gas turbine system at maximum load ramp, the poweroutput of the gas turbine system can also be increased at a lower rampthan the maximum load ramp, with the result that the steam temperaturesrise more slowly.

Since the bypass lines 100, 200 are closed at an early stage in thestartup method according to the invention and the gas and steam turbinesystem 1 is switched over into the gas and steam turbine operating modealready during the starting up of the gas turbine system 1 a to baseload, the startup operation is terminated when the gas turbine base loadis reached.

Even if the steam turbine load were to reach only a magnitude ofapproximately 80-90% when the gas turbine base load is reached, thestartup operation is deemed to be completed according to the definitionwhereby the startup operation is terminated when the base load of thegas turbine system is reached and the bypass lines are closed. Dependingon the dynamic characteristics of the heat recovery steam generator, afurther pressure increase will take place over several minutes and willbe completed after approximately 10-20 further minutes. The amount ofsteam will increase accordingly, and steam turbine power output ratingsin excess of 95% will be achieved as a function of steam temperature.

The startup method according to the invention has been described withreference to a gas and steam turbine system comprising a water-steamcycle which has only one pressure stage. It should, however, be pointedout at this juncture that the method according to the invention can alsobe applied in the case of gas and steam turbine systems which have morethan one pressure stage in the water-steam cycle. A gas and steamturbine system comprising three pressure stages, namely a high-pressurestage, a medium-pressure stage and a low-pressure stage in thewater-steam cycle, for which the startup method according to theinvention can also be used, is described for example in DE 100 04 187C1, to which reference is made in relation to the embodiment of a gasand steam turbine system comprising a plurality of pressure stages.

1. A method for starting up a gas and steam turbine system which has agas turbine system comprising a gas turbine; a steam turbine systemcomprising a steam turbine and a steam system and in which the wasteheat of a working medium expanding in the gas turbine is supplied to thesteam system for the purpose of generating steam driving the steamturbine, the method comprising: supplying a waste heat of a workingmedium of the gas turbine to the steam system to produce steam fordriving the steam turbine; and starting up the steam turbine when thefirst steam is present in the steam system and is impinged upon bysteam, wherein the gas turbine system experiences a load increase atmaximum load ramp during the entire startup operation
 2. The method asclaimed in claim 1, tuning the steam system during the startup operationin such a way that during the acceleration of the steam turbine thesteam temperature increases at a low gradient.
 3. The method as claimedin claim 1, tuning the steam system during the startup operation in sucha way that the steam pressure increases continuously.
 4. The method asclaimed in claim 3, wherein the steam system comprises a steam diverterstation, and wherein the tuning includes opening a steam diverterstation of the steam system only so wide that a minimum steam quantityrequired for accelerating and synchronizing the steam turbine isgenerated by a part of the waste heat of the working medium and anincrease in pressure is produced in the steam system by the remainder ofthe waste heat of the working medium.
 5. The method as claimed in claim3, wherein no diverter station leading to a bypassing of the steamturbine is opened in the steam system.
 6. The method as claimed in claim1, wherein the load increase is maintained until the base load of thegas turbine system has been reached.
 7. The method as claimed in claim1, wherein the gas and steam turbine system is switched over into thegas and steam turbine operating mode during the increase in load.
 8. Themethod as claimed in claim 3, tuning the steam system during the startupoperation in such a way that the steam pressure increases continuously.9. The method as claimed in claim 8, wherein the steam system comprisesa steam diverter station, and wherein the tuning includes opening asteam diverter station of the steam system only so wide that a minimumsteam quantity required for accelerating and synchronizing the steamturbine is generated by a part of the waste heat of the working mediumand an increase in pressure is produced in the steam system by theremainder of the waste heat of the working medium.
 10. The method asclaimed in claim 8, wherein no diverter station leading to a bypassingof the steam turbine is opened in the steam system.
 11. The method asclaimed in claim 2, wherein the load increase is maintained until thebase load of the gas turbine system has been reached.
 12. The method asclaimed in claim 2, wherein the gas and steam turbine system is switchedover into the gas and steam turbine operating mode during the increasein load.
 13. The method as claimed in claim 3, wherein the load increaseis maintained until the base load of the gas turbine system has beenreached.
 14. The method as claimed in claim 3, wherein the gas and steamturbine system is switched over into the gas and steam turbine operatingmode during the increase in load.